1. Field
Example embodiments relate to methods that may manage errors of data stored in memory devices.
2. Description of Related Art
A single-level cell (SLC) memory device may store one bit of data in a single memory cell. The SLC memory may be referred to as a single-bit cell (SBC) memory. A process of storing the data in a memory cell (a single-level cell) of the SLC memory may be referred to as a program process, and may change a threshold voltage of the memory cell. For example, when data of a logic value of “1” is stored in the single-level cell, the single-level cell may have a threshold voltage of 1.0 V, and when data of a logic value of “0” is stored in the single-level cell, the single-level cell may have a threshold voltage of 3.0 V.
The threshold voltage generated in each single-level cell where the same data is programmed may have a distribution within a predetermined range due to a minute electrical characteristic difference between single-level cells. For example, when a voltage read from the memory cell is higher than or equal to 0.5 V and is lower than 1.5 V, it may be determined that the data stored in the memory cell has a logic value of “1”. When the voltage read from the memory cell is higher than or equal to 2.5 V and is lower than 3.5 V, it may be determined that the data stored in the memory cell has a logic value of “0”. The data stored in the memory cell may be classified depending on the difference between currents/voltages of the memory cell during the reading operations.
Meanwhile, a multi-level cell (MLC) memory device that can store data of two or more bits in a single memory cell has been proposed in response to a need for higher integration of memory. The MLC memory device may also be referred to as a multi-bit cell (MBC) memory. However, as the number of bits programmed in the single memory cell increases, reliability may deteriorate and a read-failure rate may increase. To program ‘m’ bits in the single memory cell, any one of 2m threshold voltages may need to be generated in the memory cell. Threshold voltages of memory cells where the same data is programmed may generate a distribution within a range due to the minute electrical characteristic difference between the memory cells. A threshold voltage distribution may correspond to each of 2m data values generated by ‘m’ bits.
However, since a voltage window for a memory device may be limited, a distance between 2m distributions of threshold voltages between adjacent bits may decrease as ‘m’ increases, and the distributions may be overlapped as the distance between the distributions decreases. When the distributions are overlapped, the read-failure rate may increase.
As the MLC memory device has been widely and recently used, error control codes or error control coding or error correction codes (ECC) that detect an error occurring when storing and reading the data and correct the detected error have been actively used.